Kenneth Doherty

An Experimental Study of the Hydrodynamic Effects of Marine Growth on Wave Energy Converters

Even though the outstanding energy resource provided by ocean surface waves has long been recognized, the extraction of wave power is still in its infancy. Meanwhile, the increased interest in sustainable energy alternatives could lead to large-scale deployments of wave energy convertors (WECs) worldwide in the near future. In this context, the interaction of WECs with the marine environment is an issue that has come under increased scrutiny. In particular, the accumulation of biological deposits on the device (commonly referred to as biofouling) could lead to a modification in the behaviour and performance of the device design.For coastal devices in the North-Eastern Atlantic region, the main contributors to biofouling are likely to be the brown algae from the genus Laminaria. In the experimental study described in this paper, we have investigated the effects of algal growth on a scale model of the Oyster 800 WEC, a technology developed by Aquamarine Power. The experiments were carried out in the wave tank at Queens University Belfast. The algal growth on the device has been emulated with plastic stripes attached on the surface of the device. Several configurations with various placements and stripe dimensions were tested, in sea states typical to the targeted deployment sites. Our experiments were designed as a worst-case scenario and provide first insights into the potential effects of biofouling on the performance of a WEC. The experiments indicate that the effects of biofouling could be significant and suggest the need for further investigation.© 2013 ASME

The Development of an Experimental Force Feedback Dynamometer to Investigate the Real Time Control of an Oscillating Wave Surge Converter

An Oscillating Wave Surge Converter (OWSC) is a Wave Energy Converter (WEC) that consists of a bottom-hinged flap which oscillates due to wave action. Extensive research has been performed on this type of WEC through small scale experimental wave tank tests. One of the key challenges of experimental testing is replicating the characteristics of the Power Take-Off (PTO) system of the equivalent full scale WEC. Many scale models rely on simplified mechanical designs to simulate a PTO system. This can often restrict the experimental research into the influence of PTO design and control strategies of WECs. In order to model PTO systems and control strategies more accurately other tools are needed. This paper describes the design and build of a PLC controlled Force Feedback Dynamometer (FFD) system that enables the testing of more sophisticated control strategies applicable to an OWSC through fast application of a variable PTO damping torque. A PLC system is shown to be a viable control for PTO strategy investigations through velocity triggered damping levels. Examples of both PTO and position control strategies are presented.Copyright